Andrzej Chłopek
"The Influence of Changes of Atmospheric Air Temperaturę on the Field of Aerodynamic Potential in Mine Ventilation Net"
Prof. H Bystroń gave the definition o f aerodynamic potential O v as the difference between the value o f air pressure in selected measurement cross-section o f an underground excavation and the value o f air pressure in the same cross-section during isentropic process:
= P ~ P s = p - p 0{ l - ^ - - — [ g - ^ - z 0) + ^-(w2
< ) ] }
-k Po 2
where:
Po, p0 - pressure, density o f atmospheric air,
z, Zo - geodesic height, exact for measurement cross-section and for outset o f intake shaft, w, w0 - air velocity, exact in m easurement cross-section and in outset o f intake shaft,
k - isentropic exponent in Poisson's equation,
g - gravity acceleration.
It is assumed that changes o f tem peraturę o f atmospheric air are slow and during determination o f ąuasi-stationary field o f aerodynamic potential they can be neglected with assumption o f average values o f air density.
However, there are some practical observations (from mining experience) which show that in spite o f constant value o f difference o f aerodynamic potentials (determined correctly according to proper methodology) there were changes o f direction o f air streams.
The aim o f the w ork - research into influence o f changes o f thermal parameters o f atmospheric air (especially tem peraturę) on creation o f the field o f aerodynamic potential in mine ventilation net and into possibilities o f taking into consideration these changes to creation o f ąuasi- stationary representation o f the field.
Application o f the devices w ith constant record o f m easurement data for temperaturę, pressure and air humidity allows to determine the value o f aerodynamic potential in any selected m om ent o f the time w ithout corrections.
It allowed to give the thesis:
It is possible to determine relations describing the influence of changes of air temperaturę on the field of aerodynamic potential in mine yentilation net.
Research have been undertaken in form er “Bytom II” mine plant and they have covered the sampling o f the data (physical parameters o f atmospheric and mine air) in selected periods o f time during five measurement series (lasting from one to six weeks). THP-1 were measuring devices and they were connected with M ethane-Fire System o f the mine.
in purpose to obtain o f the States o f the field o f aerodynamic potential at 8AM, 4PM and at the midnight. Selection o f the tim e was connected with the shifts in the mine operation schedule.
As the result o f conducted analysis o f eąuations it was stated that it was purposeful to consider 15 ąuantities (considering J/m 3 and J/kg), then correlation analysis has been perform ed for them. It allowed to find the ąuantities and relations between them were under following research with application o f STATISTICA software.
Linear simple regression has been applied to describe relations between aerodynamic potential and only dry tem peraturę o f atmospheric air. M ultiple regression has been applied to describe relations between aerodynamic potential and pressure and virtual tem peraturę o f atmospheric air and mine air pressure in measuring point.
A pplication o f mixed variable (the difference o f atmospheric air pressure and mine air pressure in measuring point) allows to simplify the eąuation o f multiple regression to linear regression. Air tem peraturę is the second variable. According to this simplification - the surface diagrams (useful for visualization) have been obtained.
Basing on conducted analysis o f measurem ent data (obtained in w orking mine) following conclusions can be drawn:
1. There is strong correlation between aerodynamic potential and dry and virtual temperaturę. It indicates significant influence o f atmospheric air tem peraturę on creation o f aerodynamic potential in mine ventilation net.
2. In the case o f simple linear regression for data collected in stage 1,2 and 4 the values o f correlation coefficient were 0,7-0,86 and for fifth stage 0,62. However standard errors o f estimation had values ffom 40 to 150 J/m3 or J/kg. It indicates that during description o f the influence o f air parameters changes on the field o f aerodynamic potential changes o f air pressure must be taken into account, too, however the influence o f pressure is less than the influence o f temperaturę.
3. Five different linear fimctions w ith tw o or three variables have been considered during multiple regression analysis. In every case when regression eąuations are filled w ith air temperaturę - values o f correlation are high (higher than 0,8).
4. The influence o f changes o f atmospheric tem peraturę on the field o f aerodynamic potential is possible to describe by fimctions for every location in ventilation net. The most detailed method is with application o f two fimctions: O v = f(p0, Tvo, p) or O v = f(p0, Tvo, p).
5. During reduction o f non-stationary field o f aerodynamic potential to ąuasi-stationary field it is necessary to take into consideration not only changes o f atmospheric pressure values but also virtual temperaturę. It can be done by application o f the eąuation for correction (derived in this thesis). The correction strongly depends on difference o f geodesic heights for selected measuring points.
